The present invention relates generally to apparatus attachable to a tubular element and method of attaching the same and more particularly, but not by way of limitation, to a centralizer for a flush-joint liner and method of utilizing the same in disposing the liner in an oil or gas well for enhancing the flow of cement therealong once the liner is positioned in the well.
In drilling and completing oil and gas wells, casing is often installed to line the well bore. Sometimes a liner is also installed. The liner usually has a smaller diameter than the casing and is often of a flush-joint construction (i.e., there are no outwardly protruding collars at the joints of the liner) so that the liner can be readily lowered into the bore through the casing after the casing has been set. In this configuration, the liner partially overlaps with the casing, but otherwise it extends below the casing into a deeper region of the well.
To fix the casing or the liner in the well bore, cement is pumped down the central opening through the tubular string defining the casing or liner and back up the annulus between the outside of the string and the wall of the well bore. To space the string from the wall and to scrape the wall to insure the annulus is open around the entire string, centralizer apparatus are attached to the string prior to lowering it into the well. It is important to have the annulus open so that the cement does not channel along only part of the outside of the string, which channeling results in an improper bond whereby leaks between the bore and the string can occur. Such leaks can allow fluid to uncontrollably escape to the surface, thereby possibly creating a hazardous situation; or the leaks can allow communication of fluids between geological zones, thereby possibly detrimentally contaminating one zone with fluid from another. In addition to, or in lieu of, the use of centralizers, sometimes a liner is rotated or reciprocated during a cementing job to prevent channeling; however, this requires more sophisticated couplings between the liner and the pipe string on which the liner is run into the hole. Therefore, it is more economical if suitable centralizers can be used without requiring reciprocation or rotation to properly cement the liner.
Various types of centralizer apparatus are well known in the oil and gas industry. Some principally maintain the tubular string in a central location within the bore as the string is lowered into the bore, and others perform this centralizing function as well as scraping debris, such as wall cake, from the wall of the well bore. Some types of centralizer apparatus also are constructed with components which impart a turbulence to the cement flow so that the cement flows around the entire string as well as along it. These last types are sometimes referred to as turbolizers or turbulence-generating centralizers.
Various techniques to attach a centralizer apparatus to a string are known. The attachment of a centralizer apparatus to a string is important so that the centralizer does not come loose in the well bore and slip off a flush-joint liner, for example, into the flow path of the upper casing thereby obstructing the flow path. In the past and at present, centralizer attachment has been by a structural type of attachment, such as welding, or by a mechanical clamping technique, such as by tightening a few screws disposed around a single circumference of the centralizer or by hydraulically or pneumatically inflating a flexible element of a stop member associated with the centralizer or by pinning or bolting a split ring type of construction into engagement with the string or by mechanical stop elements retained adjacent ends of the centralizer by clamping or wedging mechanisms.
Although these various techniques have been, and currently are being, used, none has proved entirely or universally acceptable because they are either time consuming to install and not readily removable (such as with the welding technique) or they tend to come loose as the tubular string is being lowered into the well bore (such as with the mechanical clamping types of techniques). The loosening or slippage problem is particularly significant in relatively deep holes in which liners are used because higher pressures exerting forces exceeding the holding capacity of the prior art techniques can be encountered.
Therefore, there is the need for an apparatus readily attachable to, and preferably subsequently readily removable from, a tubular string so that the apparatus will not come off in the high pressure environments before they are intended to come off. There is also the need for a method of attaching these apparatus and of removing the apparatus. More specifically, there is the need for an improved centralizer apparatus for a flush-joint liner and a method of attaching the same so that it will not come off in response to forces encountered in the well bore, such as from high pressures or movement of the string.